VoIP is the transport of voice traffic using the Internet Protocol (IP). In the mobile world, VoIP means using a packet-switched (PS) service for transport of Internet Protocol (IP) packets which contain, e.g., Adaptive Multi-Rate (AMR) codec speech frames for voice mobile phone calls. A packet-switched connection is often simply referred to as a data connection.
Circuit-switched networks use circuit switching for carrying voice traffic where the network resources are statically allocated from the sender to receiver before the start of the message transfer, thus creating a “circuit.” The resources remain dedicated to the circuit during the entire message transfer and the entire message follows the same path. While this arrangement works quite well to transfer voice, IP is an attractive choice for voice transport for many reasons including lower equipment costs, integration of voice and data applications including multi-media like email, instant messaging, video, the world wide web, etc., lower bandwidth requirements, and the widespread availability of IP.
As VoIP becomes more accepted and commonplace, some users will likely upgrade from an existing circuit-switched phone to a VoIP phone. It is likely that each such upgrading user will bring a benefit for the operator in terms of increased hardware efficiency.
In packet-switched networks, the message is broken into packets, each of which can take a different route to the destination where the packets are recompiled into the original message. The packet switched (PS) service utilized for VoIP can be, for example, GPRS (General Packet Radio Service), EDGE (Enhanced Data Rates for Global Evolution), or WCDMA (Wideband Code Division Multiple Access). Each of these example services happen to be built upon the Global System for Mobile communications (GSM), a second generation (“2G”) digital radio access technology originally developed for Europe. GSM was enhanced in 2.5G to include technologies such as GPRS. The third generation (3G) comprises mobile telephone technologies covered by the International Telecommunications Union (ITU) IMT-2000 family. The Third Generation Partnership Project (3GPP) is a group of international standards bodies, operators, and vendors working toward standardizing WCDMA-based members of the IMT-2000.
EDGE (or Enhanced Data Rates for Global Evolution) is a 3G technology that delivers broadband-like data speeds to mobile devices. EDGE allows consumers to connect to the Internet and send and receive data, including digital images, web pages and photographs, three times faster than possible with an ordinary GSM/GPRS network. EDGE enables GSM operators to offer higher-speed mobile-data access, serve more mobile-data customers, and free up GSM network capacity to accommodate additional voice traffic. EDGE uses the same TDMA (Time Division Multiple Access) frame structure, logical channels, and 200 kHz carrier bandwidth as GSM networks, which allows existing cell plans to remain intact.
In EDGE technology, a base transceiver station (BTS) communicates with a mobile station (e.g., a cell phone, mobile terminal or the like, including computers such as laptops with mobile termination). The base transceiver station (BTS) typically has plural transceivers (TRX). A time division multiple access (TDMA) radio communication system like GSM, GPRS, and EDGE divides the time space into time slots on a particular radio frequency. Time slots are grouped into frames, with users being assigned one or more time slots. In packet-switched TDMA, even though one user might be assigned one or more time slots, other users may use the same time slot(s). So a time slot scheduler is needed to ensure that the time slots are allocated properly and efficiently.
Traditionally, time slots for data packet connections are allocated assuming an asymmetry between the uplink (mobile-to-network) and downlink (network-to-mobile). Thus, time slot allocation schemes have been used that optimize for that asymmetry. Example asymmetric data packet connections include: File Transfer Protocol FTP downloading (asymmetric in the downlink), web page download (downlink), streaming download (asymmetric in the downlink), multimedia messaging services (MMS) (asymmetric in the downlink for reception and asymmetric in the uplink for sending), and ping-pong type services (asymmetric first in the uplink, then asymmetric in the downlink). Example asymmetric scheduling methods for GPRS include “Weighted Round Robin” and “Virtual Clock Multiplexing.” In contrast, VoIP service is symmetrical in the downlink and uplink. Because current radio resource/channel allocation schemes are tailored for asymmetrical services, they are not optimal for symmetrical services like VoIP.